This invention is directed to various innovations in snowmobile design, including a modular front suspension system and a stabilizer assembly, a lightweight frame structure and a drive train that reduces the center of gravity of the snowmobile.
Snowmobile design has incrementally moved towards more powerful motors, with a resulting increase in the weight of the machines due to the larger motor and corresponding support structure. Frequently, increased weight results in a higher center of gravity of the snowmobile. Increased weight and increased center of gravity can have a detrimental affect on the ride quality and handling characteristics of the snowmobile.
Handling, cornering and ride quality are largely dependent upon the front suspension system of the snowmobile. It is common practice to suspend the skis of a snowmobile independently by means of respective strut type suspensions. It is desirable to provide some form of stabilizer or sway bar arrangement interconnecting the front skis to reduce the amount of leaning that occurs during cornering of the snowmobile. Due to the rough and sometimes uncertain terrain over which snowmobiles are ridden, it is desirable that the stabilizer arrangement be positioned so that it will be protected if unexpected objects are encountered, such as disclosed in U.S. Pat. No. 4,690,234 (Takada).
U.S. Pat. No. 4,489,954 discloses an anti-roll mechanism that includes a torsion bar supported by the body that is connected to the skis for torsion loading upon independent movement of the skis relative to the body. The connection between each of the skis and the torsion bar is such that the torsion bar is loaded by the pivotal movement of the skis about their steering axes for providing a self-centering force on the skis.
U.S. Pat. No. 4,671,521 (Talbot, et al) discloses a snowmobile ski suspension including upper and lower transverse suspension arms vertically spaced and each having an outboard end articulated to a ski spindle and an inboard end articulated to a fixed mounting on the frame of the snowmobile. The upper and lower transverse suspension arms define a parallelogram linkage for guiding the spindle to move generally vertically with respect to the snowmobile.
U.S. Pat. No. 5,029,664 (Zuwalski) discloses a suspension system with a geometry that includes upper and lower suspension linkages of predetermined lengths in cooperation with a spindle of a predetermined length for eliminating lateral movement of the skis during suspension travel. The respective linkages and spindles are interconnected by ball joints at predetermined locations in such a manner that during deflection of the suspension system, a ski attached to the lower end of the spindle moves substantially in a line parallel to a vertical plane which contains the longitudinal axis of the snowmobile.
What is needed is a snowmobile design that provides a high power-to-weigh ratio while maintaining optimum handling characteristics and ride quality.
The present invention is directed to various innovations in snow mobile design. In one embodiment, the snowmobile includes a modular front suspension system and a stabilizer assembly. In another embodiment, the frame structure includes a lightweight frame structure. In yet another embodiment the snowmobile includes a drive train that reduces the center of gravity. Finally, all of these features are combined on a single snowmobile.
The present invention is directed to a modular front suspension system for a snowmobile that is substantially self-contained and self-supporting. The present modular front suspension system is assembled around a primary support structure, such as an extrusion or other structural member. The primary support structure can be easily attached to, or detached from, the snowmobile frame. The modularity of the present suspension system decreases assembly costs.
The front suspension system of a snowmobile is typically assembled directly to the frame of the snowmobile. The present modular front suspension system can be assembled independently of the snowmobile and conveniently transported or stored for later use. The self-contained, self-supporting nature of the present suspension system allows for lower cost assembly, machine handling and automated testing.
Repairs on conventional snowmobile suspension systems are often accomplished by replacing individual components. End-users, however, typically lack the proper equipment to determine whether the front suspension system is operating properly. The present front suspension system can be easily removed by the user and returned to the manufacturer for factory repair. A temporary or permanent replacement suspension systems can also be sent to the customer for easy installation.
Additionally, a standardized primary support structure can be utilized so that a variety of suspension systems with different features can be easily substituted on the snowmobile by the manufacture the dealer or the end-user. Since the front suspension system is less expensive than the entire snowmobile the manufacturer/dealer can offer a variety of options with lower inventory costs. The end-user may also purchase multiple front suspension systems for a single snowmobile. For example, the end-user may have one front suspension system for racing and another for touring.
In one embodiment, the modular front suspension system includes a primary support structure having first and second ends a center opening and at least one mounting surface attachable to the chassis. A pair of upper control arms are pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively. A pair of lower control arms are pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively. A pair of ski spindle housings are pivotally connected to distal ends of the upper and lower control arms, respectively. The ski spindle housings are connectable to the steerable skis. A stabilizer assembly is mechanically coupled to the ski spindle housings. In one embodiment the stabilizer assembly extends through the center opening and is mechanically coupled to the ski spindle housings.
In another embodiment, the modular front suspension system includes a primary support structure having first and second ends, a center opening and at least one mounting surface attachable to the chassis. A pair of upper control arms are pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively. A pair of lower control arms are pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively. A pair of ski spindle housings are pivotally connected to distal ends of the upper and lower control arms respectively. The ski spindle housings are connectable to the steerable skis. A pair of shock mounts are pivotally attached to one of the upper control arm or primary support structure, respectively. A pair of shock absorber are attached to the shock mounts and the spindle housings, respectively.
The present invention is also directed to a stabilizer assembly for use in a front suspension system on a snowmobile. The present stabilizer assembly may be used with or without the present modular front suspension system.
To provide flat cornering on smooth terrain, the front suspension system initially provides stiff resistance to ski displacement. In the event that rough terrain is encountered, subsequent ski displacement is preferably less stiff. That is, the force per unit displacement decreases with greater displacement. For example, the front suspension system provides stiff resistance to ski displacement during high-speed turns. If bumps are encountered during the turn, the front stabilizer system provides less resistance to ski displacement as compared to its initial movement. In one embodiment, the force per unit displacement curve is a step function with greater force per unit displacement required during initial displacement and less additional force per unit displacement for subsequent displacement.
In one embodiment, the present stabilizer system includes first and second stabilizer brackets attached to the control arms, respectively. A rocker arm having first and second ends is pivotally mounted to the snowmobile. A first stabilizer member assembly is pivotally connected to the first stabilizer bracket and the first end of the rocker arm. A second stabilizer member assembly is pivotally connected to the second stabilizer bracket and the second end of the rocker arm. The stabilizer system transfers load from one side of the snowmobile to another. That is, spring force from one side of the snowmobile is transferred to the side experiencing the greatest ski displacement. In one embodiment, the actual spring rate on the stabilizer member assemblies can be different from ski to ski.
In one embodiment, the stabilizer member assembly includes an extendable rod assembly having a maximum extension and a spring cap fixed thereto. A sleeve is slidably engaged with the extendable rod assembly adjacent to the first stabilizer bracket. A spring is arranged around the extendable rod assembly and interposed between the spring cap and the sleeve. In one embodiment, an adjustment mechanism is provided for sliding the sleeve along the extendable rod assembly to apply a bias of the spring. The extendable rod assembly is typically a telescoping structure. The stabilizer member assemblies are typically in a fully extended or topped-out configuration in a level or horizontal resting state.
The stabilizer member assemblies can be configured to provide a preload in the horizontal resting state such that initial upward displacement of one of the skis is resisted by a first force, and subsequent upward displacement of that ski is resisted by the addition of a second force proportionally less than the first force. In another embodiment, the first stabilizer member assembly is a double-acting spring assembly and the second stabilizer members assembly comprises a rigid shaft.
The present modular front suspension system and the present stabilizer assembly have application in other vehicles, such as automobiles, trucks and all-terrain vehicles.
The present invention is also directed to a chassis for a snowmobile having an endless belt drive system. The chassis includes a plurality of front structural members defining a motor compartment. Front suspension system mounting locations are positioned on distal ends of two or more of the front structural members. A pair of independent, rear structural members are rigidly connected to the front structural members and extend rearwardly from the motor compartment on opposite sides of an endless belt channel. A protective shell extends between the pair of rear structural members and over the endless belt channel. In one embodiment, the protective shell comprises a lightweight, resin based material that transfers substantially no loads between the pair of rear structural members. The snowmobile chassis further includes a rear suspension system extending between the pair of rear structural members. The rear suspension system transfers substantially all loads between the pair of rear structural members.
In one embodiment, the snowmobile chassis includes a motor located in the motor compartment. The motor has at least one carburetor positioned on a first side of the motor adjacent to the front suspension system mounting locations and an exhaust port positioned on a second side of the motor.
The present invention is also directed to a snowmobile chassis having a motor compartment and an endless belt channel. A motor is located in the motor compartment. The motor has at least one carburetor positioned on a first side of the motor adjacent to a front suspension system and an exhaust port positioned on a second side of the motor. The motor has a drive clutch. A driven pulley is located on a gearbox that is located adjacent to the endless belt channel. An endless belt drive shaft is located in the endless belt channel and mechanically coupled directly to the gearbox. A drive belt mechanically couples the drive clutch to the driven pulley. A torque arm connects the driven pulley to the snowmobile chassis.